Control channel detection method and apparatus of mimo system

ABSTRACT

A control channel transmission/reception method and apparatus are provided. The control channel transmission method of a base station includes acquiring a criterion for sorting control channels, sorting the controls channels into at least two control channel sets based on the criterion, configuring the control channels by allocating at least one antenna port to each control channel set, and transmitting the control channels as configured.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a Koreanpatent application filed on Nov. 7, 2011 in the Korean IntellectualProperty Office and assigned Serial No. 10-2011-0115276, the entiredisclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Multiple Input Multiple Output (MIMO)system. More particularly, the present invention relates to a method andapparatus for detecting control channels in a MIMO system.

2. Description of the Related Art

Mobile communication systems are developed to provide subscribers withvoice communication services on the move. With the rapid advance oftechnologies, the mobile communication systems have evolved to supporthigh speed data communication services as well as the standard voicecommunication services. However, the limited resource and userrequirements for higher speed services in the current mobilecommunication system spur the evolution to more advanced mobilecommunication systems.

Long Term Evolution—Advanced (LTE-A) is a next generation mobilecommunication standard under development to meet such user requirements.LTE-A is being standardized by the 3^(rd) Generation Partnership Project(3GPP). LTE-A is a technology for realizing high speed packet-basedcommunication at up to about 1 Gbps. In an effort to achieve this,discussions are being held on several schemes such as networkmultiplexing for deploying multiple evolved Node Bs (eNBs) overlappinglyin a specific area and increasing the number of frequency bandssupported by an eNB.

Meanwhile, LTE operates with control channels designed based on adistributed transmission mode. The distributed transmission-based designaims to reduce inter-cell interference, distribute interference, andachieve frequency diversity gain.

However, LTE-A assumes there is an operating environment with very shortinter-cell distance and high inter-cell interference. Accordingly, inthe distributed transmission mode-based control channel design,inter-cell interference is inevitable.

LTE-A is also capable of adopting a control channel transmission modeexploiting frequency-selective gain. This is advantageous in that thecontrol channel can be transmitted using a lesser amount of resources,but is also disadvantageous in that the terminal is likely to fail toreceive the control channel, especially when the channel variesfrequently. The evolved system supports both the related-art frequencydiversity gain-oriented transmission mode and frequency selectivegain-oriented transmission mode. The frequency-selective gain variesdynamically according to the status of the terminal Also, there can be acontrol channel to which only one of the two transmission modes isemployed, i.e., frequency-selective gain-oriented and frequencydiversity gain-oriented transmission modes.

Accordingly, the system should support both the aforementionedtransmission modes, frequency-selective gain-oriented and frequencydiversity gain-oriented transmission modes, in control channeltransmission without compromising terminal complexity. This means thatthere is a need of a control channel detection method for the terminalto acquire the configuration information on the new control channelstructure.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to address the aboveproblems and it is an object of the present invention to provide acontrol channel detection method and apparatus that is capable oftransmitting/receiving the control channels configured with differentreference signals and/or in different transmission modes.

In accordance with an aspect of the present invention, a control channeltransmission method of a base station is provided. The method includesacquiring a criterion for sorting control channels, sorting the controlchannels into at least two control channel sets based on the criterion,configuring the control channels by allocating at least one antenna portto each control channel set, and transmitting the control channels asconfigured. In accordance with another aspect of the present invention,a control channel reception method of a terminal includes acquiring acriterion for sorting control channels into at least two control channelsets, acquiring allocation information on at least one antenna portallocated to each control channel set sorted by the criterion, andreceiving the control channels based on the criterion and allocationinformation.

In accordance with an aspect of the present invention, a control channelreception method of a terminal is provided. The method includesacquiring a criterion for sorting control channels into at least twocontrol channel sets, acquiring allocation information on at least oneantenna port allocated to each control channel set sorted by thecriterion, and receiving the control channels based on the criterion andallocation information.

In accordance with another aspect of the present invention, a basestation for transmitting control channels is provided. The base stationincludes a scheduler which acquires a criterion for sorting the controlchannels and sorts the controls channels into at least two controlchannel sets based on the criterion, a control channel informationgenerator which configures the control channels by allocating at leastone antenna port to each control channel set, and a transmitter whichtransmits the control channels as configured.

In accordance with still another aspect of the present invention, aterminal for receiving control channels is provided. The terminalincludes a controller which acquires a criterion for sorting controlchannels into at least two control channel sets and acquires allocationinformation on at least one antenna port allocated to each controlchannel set sorted by the criterion, and a receiver which receives thecontrol channels based on the criterion and allocation information.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating a control channel structure of asubframe for use in a Long Term Evolution (LTE) system to whichexemplary embodiments of the present invention are applied;

FIG. 2 is a diagram illustrating a control channel structure of anLTE-Advanced (LTE-A) system according to an exemplary embodiment of thepresent invention;

FIG. 3 is a diagram illustrating a control channel-resource mappingmechanism according to an exemplary embodiment of the present invention;

FIG. 4 is a diagram illustrating a mechanism of a control channeltransmission according to a first exemplary embodiment of the presentinvention;

FIG. 5 is a diagram illustrating a mechanism of a control channeldetection according to a second exemplary embodiment of the presentinvention;

FIG. 6 is a diagram illustrating a mechanism of a control channeldetection according to a third exemplary embodiment of the presentinvention;

FIG. 7 is a flowchart illustrating a control channel transmission methodof an evolved Node B (eNB) according to an exemplary embodiment of thepresent invention;

FIG. 8 is a flowchart illustrating a control channel reception method ofa User Equipment (UE) according to an exemplary embodiment of presentinvention;

FIG. 9 is a block diagram illustrating a configuration of a controlchannel transmission apparatus of an eNB according to an exemplaryembodiment of the present invention; and

FIG. 10 is a block diagram illustrating a control signal receptionapparatus of a UE according to an exemplary embodiment of the presentinvention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in this description and the appended claims arenot to be interpreted in common or lexical meaning but, based on theprinciple that an inventor can adequately define the meanings of termsto best describe the invention, to be interpreted in the meaning andconcept conforming to the technical concept of the present invention.

Although the description is directed to the exemplary case of Long TermEvolution (LTE) and LTE-Advanced (LTE-A) systems, the present inventioncan be applied to other radio communication systems operating with basestation scheduling.

Orthogonal Frequency Division Multiplexing (OFDM) is a transmissiontechnique for transmitting data using multiple carriers, i.e., amulticarrier data transmission technique which parallelizes the serialinput stream into parallel data streams and modulates the data streamsonto the orthogonal multiple carriers, i.e., sub-carrier channels.

The multicarrier modulation scheme originated in the late 1950's withmicrowave radio for military communication purposes, and OFDM usingorthogonal overlapping multiple subcarriers was developed in 1970's.However, the implementation of such systems was limited due to thedifficultly of implementing orthogonal modulations between multiplecarriers. With the introduction of the idea of using a Discrete FourierTransform (DFT) for implementation of the generation and reception ofOFDM signals, by Weinstein, in 1971, OFDM technology began a period ofrapid development. Additionally, the introduction of a guard interval atthe start of each symbol and the use of a Cyclic Prefix (CP) addressesthe negative effects caused by multipath signals and delay spread.

Owing to such technical advances, the OFDM technology is applied invarious digital communications fields such as Digital Audio Broadcasting(DAB), Digital Video Broadcasting (DVB), Wireless Local Area Network(WLAN), and Wireless Asynchronous Transfer Mode (WATM). That is, theimplementation of OFDM could be accomplished by reducing implementationcomplexity with the introduction of various digital signal processingtechnologies such as Fast Fourier Transform (FFT) and Inverse FastFourier Transform (IFFT).

OFDM is similar to Frequency Division Multiplexing (FDM) but much morespectrally efficient for achieving high speed data transmission byoverlapping multiple subcarriers orthogonally. Due to the spectralefficiency and robustness to the multipath fading, OFDM has beenconsidered as a prominent solution for broadband data communicationsystems.

Other advantages of OFDM are to control Inter-Symbol Interference (ISI)using a guard interval and to reduce the complexity of an equalizer inview of hardware as well as spectral efficiency and robustness to thefrequency selective fading and multipath fading. OFDM is also robust toimpulse noise so as to be employed in various communication systems.

In wireless communications, high-speed, high-quality data services aregenerally hindered by the channel environment. In wirelesscommunications, the channel environment suffers from frequent changesnot only due to Additive White Gaussian Noise (AWGN), but also powervariation of received signals, caused by a fading phenomenon, shadowing,a Doppler effect brought by movement of a User Equipment (UE) and afrequent change in a velocity of the UE, interference by other users ormultipath signals, etc. Therefore, in order to support high-speed,high-quality data services in a wireless communication system, there isa need to efficiently address the above channel quality degradationfactors.

In OFDM, modulation signals are located in two-dimensionaltime-frequency resources. Resources on the time domain are divided intodifferent OFDM symbols, and are orthogonal with each other. Resources onthe frequency domain are divided into different tones, and are alsoorthogonal with each other. That is, the OFDM scheme defines one minimumunit resource by designating a particular OFDM symbol on the time domainand a particular tone on the frequency domain, and the unit resource isreferred to as a Resource Element (RE). Since different REs areorthogonal with each other, signals transmitted on different REs can bereceived without causing interference to each other.

The physical channel is a channel defined on the physical layer fortransmitting modulation symbols obtained by modulating one or more codedbit sequences. In an Orthogonal Frequency Division Multiple Access(OFDMA) system, a plurality of physical channels can be transmitteddepending on the usage of the information sequence or receiver. Thetransmitter and receiver determine REs on which a physical channel istransmitted, and this process is referred to as mapping.

The LTE system and LTE-A system evolved therefrom are the representativesystems adopting OFDM in a DownLink (DL). Meanwhile, the LTE/LTE-Asystem adopts Single Carrier-Frequency Division Multiple Access(SC-FDMA) in UpLink (UL).

FIG. 1 is a diagram illustrating a control channel structure of asubframe for use in an LTE system to which exemplary embodiments of thepresent invention are applied. The subframe of FIG. 1 may be compatiblein the LTE-A system.

Referring to FIG. 1, the entire downlink transmission bandwidth 101consists of a plurality of Resource Blocks (RBs) (also referred toherein as Physical RBs (PRBs)). Each RB 103 consists of 12 frequencytones arranged in the frequency domain and 14 or 12 OFDM symbolsarranged in the time domain. A RB is the basic unit of resourceallocation. FIG. 1 is directed to a subframe consisting of 14 timesymbols. Each subframe 105 spans 1 ms and consists of two 0.5 ms slots107.

Reference Signals (RSs) 113 and 115 are signals agreed upon between anevolved Node B (eNB) and a User Equipment (UE) for use in channelestimation. There are two types of reference signals, i.e., a Common RS(CRS) 115 and a Dedicated RS (DRS) 113, defined for use in the LTEsystem. The eNB with two antennas transmits CRS through ports 0 and 1.The eNB with 4 antennas transmits the CRS 115 through ports 0, 1, 2, and3. If there is more than one antenna port, this means that amulti-antenna system is employed.

The RSs are arranged at fixed positions of the RB in a cell-specificmanner at a regular interval in the frequency domain. That is, the RSsfor the same antenna port are located on every 6^(th) RB, and the reasonwhy the absolute positions of the RSs are determined differently percell is to avoid collisions between the RSs of different cells. Thenumber of RSs differs according to the antenna port. For the antennaports 0 and 1, a total of 8 RSs exist in a single RB or subframe, whilefor the antenna ports 2 and 3, a total of 4 RSs exist in a single RB orsubframe. Since it has to be received by all UEs, the CRS is transmittedin all RBs across the entire downlink bandwidth.

The DRS 113 is a UE-specific reference signal transmitted in the RBwhere the UE is scheduled. If the RB receiving the corresponding RB 117does not use DRS, no DRS is transmitted. The DRS 115 can also betransmitted through multiple ports like the CRS. Although it depends onthe configuration, the LTE-A system may use the same resource for twoantenna ports differentiated with two scrambling codes and may supportup to 8 DRSs. The DRS is transmitted in the data region 103 of aspecific PRB assigned to a specific UE but not across the entiredownlink bandwidth 101.

Typically, the common reference signal can be used for a single antennatransmission or a Transmission Diversity (TD) transmission mode forachieving frequency or antenna diversity gain, along with a beamformingtechnique. Typically, the CRS is receivable by all users within the celland thus the signals are carried in the CRS by all UEs.

In order to provide the frequency selective gain with the DRS-basedtransmission, a beamforming technique is used. Since the eNB performstransmission using the UE-recommended frequency resource, it is possiblefor the UE to receive the signal with high quality. However, there is ashortcoming in that it is vulnerable to a fast channel varyingenvironment.

The control channel signal of LTE is arranged at the beginning of asubframe in the time domain. The control channel signal can be locatedin the control channel region 109 in FIG. 1. The control channel signalcan be transmitted across N OFDM symbols at the beginning of thesubframe. N can be 1, 2, or 3. In the case where the transmissionbandwidth is narrow, n can be 2, 3, or 4. FIG. 1 is directed to the casewhere the control channel region of N=3. The control channel region 109can be changed dynamically at every subframe. If one OFDM symbol issufficient due to there being a small amount of control channel data, itis possible to allocate the first OFDM symbol for the control channelsignal transmission (N=1) while the remaining 13 OFDM symbols areallocated for data channel signal transmission. If the control channelamount increases, the number of symbols available for data transmissiondecreases. N is used as the basic information for allocated controlchannel resource de-mapping and is especially used for interleaving ofthe control channel. The reason for placing the control channel signalat the beginning of the subframe is for early detection of the controlchannel such that the UE determines whether to perform a data channelreception operation depending on the presence of the data channel signaladdressed to the current UE. If there is no data channel signaladdressed to the UE, it is not necessary for the UE to attempt datachannel decoding, thereby avoiding the power consumption caused by datachannel reception. Also, by receiving the control channel at thebeginning of the subframe prior to the data channel, it is possible toreduce scheduling delay.

In LTE, a Physical Dedicated Control Channel (PDCCH) is a physicalchannel for transmitting a common control channel and a dedicatedcontrol channel including data channel allocation information,allocation information for system information transmission or powercontrol information. The eNB having one antenna transmits the PDCCH in asingle antenna transmission mode, while the eNB having multiple antennastransmits the PDCCH in a Transmit Diversity (TD) mode.

The eNB can configure the PDCCH with different channel coding ratesdepending on the channel state of the UE. Since Quadrature Phase ShiftKeying (QPSK) is fixedly used for PDCCH transmission, the resourceamount is changed in order to change the channel coding rate. The UEwith a good channel condition uses a high channel coding rate to reducethe amount of resources used for transmission. Meanwhile, the UE with abad channel condition uses a low channel coding rate to ensure that thesignal may be received despite the use of a greater amount of resources.The amount of resources for each PDCCH is determined depending on theunit of a Control Channel Element (CCE). A CCE consists of a pluralityof Resource Element Groups (REGs). The REG of a PDCCH is interleaved toensure diversity and distribute inter-cell interference and then mappedto the control channel region of PRBs across the entire downlinkbandwidth as denoted by reference number 101 and 109.

The interleaving is performed to all of the REGs of the subframe thatare determined by N. The output of the control channel interleaving isdesigned to space the REGs of the control channel allocated across oneor more symbols far enough to acquire diversity gain while avoidinginter-cell interference caused by use of the same interleaver for thecells. Also, it guarantees uniform distribution of the REGs constitutingthe same channel across the per-channel symbols. Also, it is multiplexedwith other control channels.

In the advanced environment experienced in the recent LTE-A system,however, it is assumed to deploy a large number of eNBs that aredifferent in size within an area as compared to the related-art system.This increases interference per unit square such that the PDCCH designedfor preventing inter-cell interface fails to adequately mitigateinterference and is influenced more by interference from neighbor cells,resulting in a reduction of UE coverage.

Furthermore, the eNB adopting a Multi-User Multiple Input MultipleOutput (MU-MIMO) technique for scheduling a greater number UEs andmaximizing the system throughput lacks control channel capacity whilehaving a sufficiently large data channel, resulting in a schedulingfailure. In order to address this problem, there is a need to study thetransmission of a control channel using a dedicated reference signal onthe legacy data channel. In the case of transmitting the control channelon the data channel, it is possible to avoid inter-cell interference andutilize the dedicated reference signal and, as a consequence, multipleantennas can be used to transmit the control channel for multiple UEs onthe same resource, resulting in a maximization of the control channelcapacity. This new control channel is referred to as an enhanced PDCCH(ePDCCH) and may, for example, be found in control channel region 111 inFIG. 1.

FIG. 2 is a diagram illustrating a control channel structure of an LTE-Asystem according to an exemplary embodiment of the present invention.The control channel of LTE-A includes a PDCCH transmitted with CRS 209and an ePDCCH transmitted at locations in the data region 207. Since theePDCCH 213 is mapped to the resources of the data region, it can betransmitted with DRS. The ePDCCH 213 is also capable of beingtransmitted with CRS 209, a UE group reference signal, or a sub-bandreference signal. The UE group reference signal denotes the commoncontrol channel shared by a set of UEs. The sub-band reference signal isa common reference signal but is smaller in the frequency or time domainthan the CRS 209. The sub-band reference signal is carried in some RBsor subframes 205.

The PDCCH is capable of being transmitted in the single antennatransmission mode and/or the TD transmission mode. The ePDCCH can betransmitted with various reference signals in at least one of thebeamforming transmission mode, the single antenna transmission mode, andthe TD transmission mode. The PDCCH is mapped to the regions 211distributed across the PRBs 203 constituting the entire downlinkbandwidth 201. The eNB is capable of restricting some resources to thefrequency-selective region and some resources to the frequencydiversity-guaranteed region such that the ePDCCH is transmitted in theregion 213. The eNB is capable of changing the ePDCCH transmission modeaccording to the UE status, and the PDCCH reception probability alsoinfluences the reception of the ePDCCH.

The PDCCH can be classified into one of a common control channel and adedicated control channel. The common control channel region is of acontrol channel to which all UEs attempt control channel demodulation.The dedicated control channel region is of the control channel to whicha specific UE attempts control channel demodulation. In the LTE system,the control channel has no fixed code rate but its amount of informationis determined according to the aggregation level. The common controlchannel is limited to aggregation levels 4 and 8, while the dedicatedcontrol channel is limited to aggregation levels 1, 2, 4, and 8. Theunit of aggregation is CCE. The aggregation level 4 allows for the useof up to 4 regions, while the aggregation 8 allows for the use of up to2 regions. Accordingly, the eNB is capable of transmitting the commoncontrol channel at up to 6 regions. The number of demodulations for theUE-specific control channel is also determined according to theaggregation level. There can be up to 6 types for aggregation levels 1and 2 and up to 2 types for aggregation levels 4 and 8. The CCEs onwhich the modulation is taken are identical with each other or notaccording to the aggregation level. Table 1 shows the number of PDCCHcandidates according to the aggregation level and control channel type.

TABLE 1 Search space S_(k) ^((L)) # of PDCCH Aggregation Size candidatesType level L [in CCEs] M^((L)) UE- 1  6 6 specific 2 12 6 4  8 2 8 16 2Common 4 16 4 8 16 2

The control channel transmitted in the logical resource region betweenthe eNB and the UE is determined according to Equation (1):

L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i,

m=0, . . . ,M ^((L))−1,i=0, . . . ,L−1  (1)

where L denotes aggregation level, and N_(cce,k) denotes a total numberof CCEs existing in the k^(th) subframe. With Equation (1), the UE iscapable of acquiring CCE index for blink demodulation of the controlchannel transmitted by the eNB. Y_(k) denotes a random variable fordistributing the control channels over the entire control channel regionper user to avoid collision of control channels and changes at everysubframe by Equation (2). In the case of the common control channel,however, Y_(k) is set to 0 such that all UEs can receive. Y_(k) startswith UE ID; and A and D are 39826 and 65537 respectively.

Y _(k)=(A·Y _(k-1))mod D  (2)

FIG. 3 is a diagram illustrating a control channel-resource mappingmechanism according to an exemplary embodiment of the present invention.The common control channel 301 and UE-specific control channel 303 areinterleaved by the interleaver 305. The interleaved signal isdistributed across the entire bandwidth 307 in the unit of a REG The UE,using CRS port #0˜#309 maps the control channel resources into logicalresources 310. The common control channel 313 is located at thebeginning of the logical resource region 311 and is actually transmittedin the UE-specific transmission region among the candidates of theresource region. The UE-specific control channels 315 and 317 aretransmitted in the UE-specific transmission regions of the same logicalresource region. The UEs use different, overlapped, or the same logicalregion at every subframe. This is to avoid repeated collisions of thecontrol channel regions of the UEs.

In the case of the PDCCH, since the UEs receive the control channelswith a common reference signal, all control channels are transmitted inthe region 315 or 317 in the same transmission mode and with samereference signals. In the case of ePDCCH, however, the control channelscan be transmitted in different transmission modes and with differentresources, there is a need for configuring respective transmission modesand determining respective search spaces. A search space configurationmethod is proposed hereinafter.

FIG. 4 is a diagram illustrating a mechanism of a control channeltransmission according to a first exemplary embodiment of the presentinvention. According to the first exemplary embodiment of the presentinvention, the eNB sorts the control channels mapped to a controlchannel resource into sets by control channel format or type andtransmits the sets of different formats or types with differentreference signals or different reference signals ports. The terminalreceives the control channels of the sets of different formats or typesin the search regions for the different reference signals or referencesignal ports.

The control channel groups 401 and 411 sorted by control channel formator control channel property are depicted. The eNB is capable of sortingthe control channels into groups by format. For example, the eNB iscapable of sorting the control channels into 3/3A, 1A, 1C, and otherformat groups. The eNB is also capable of sorting the control channelsinto a group of control channels for multiple UEs and a group of controlchannels for a single UE. The control channels also can be sorted into agroup of control channels transmitted with a UE's unique Radio NetworkTemporary Identifier (RNTI) and a group of control channels transmittedwith the RNTI for system information, paging, initial access, and powercontrol. The eNB may notify the UE of the identifiers of the controlchannel groups through higher layer signaling. According to a modifiedexemplary embodiment, the control channel group identifiers can bestored in the memories of the UE and the eNB according to apredetermined rule.

The control channel groups are encoded by the respective encoders 403and 413. The eNB arranges the control channels in a resource group 405signaled by the eNB. The eNB notifies the UE of the information on thereference signals used in the respective control channel groups. Forexample, the reference signal information 407 is used for transmittingthe control channel group 401, and the reference signal information 417is used for transmitting the control channel group 411. The controlchannel groups can be transmitted via respective antennas 409 and 421 indifferent transmission modes. Depending on the properties of the controlchannel groups, one control channel group can transmitted in a TD mode,while the other control channel group in a beamforming mode. Here, thecontrol channel groups 401 and 411, the resource group 405, and thereference signal information 407 and 417, is collectively denoted as410.

For another example, one control channel group can be transmitted viaantenna 409 as precoded by the precoder 408, while the other controlchannel group can be transmitted via antenna 421 as precoded by theprecoder 419. Although both the control channel groups are processed inthe same transmission mode, they may be transmitted with differentprecodings. It is also possible for a control channel group to beallocated one reference signal or multiple reference signals. In the TDtransmission mode, if two or more reference signal groups are allocatedto the control channel group and beamforming is used, one or tworeference signal groups are allocated for the control channel group. Thereference signal information 407 and 417 can be notified through higherlayer signaling and, according to a modified exemplary embodiment, theUE is capable of performing blind demodulation on the reference signalinformation 407 and 417. In the blind demodulation, the terminalattempts demodulation with the assumption of all available combinationsof the transmission modes and reference signals until the controlchannel is received successfully.

The UE receives the control channel resource region informationtransmitted by the eNB through higher layer signaling and reconfiguresthe control channels into logical control channel region 423. Theterminal configures two search spaces based on the information of thetwo control channel groups and the reference signals for use inreceiving the control channel groups. The first search space is thesearch space 425 for the first control channel group in which the UEsearches for the control signal using the reference signal group 407.The second search space is for second control channel group in which theUE searches for the control signal using the second reference signalgroup 417.

If the first control channel group is of controls channels for multipleUEs, the UEs receive the control channels using the same referencesignal. The UEs receive the control channels 411 using differentreference signals in the different control channel search spaces 431,427, and 429. In the case where the same resource is allocated to theUEs as denoted by reference number 431 and 427, the control channels canbe transmitted with different reference signals. In the case where thedifferent resources are allocated to the UEs as denoted by referencenumber 431 and 429, the control channel can be transmitted with the samereference signal. In this way, the eNB is capable of transmitting thecontrol channels in different transmission modes according to the UEstatus and type of the control channels. If the number of UEs which hasto receive the current control channel decreases to 1, the eNB iscapable of changing the transmission mode dynamically for the UE toreceive the control channel efficiently.

A description is made of the search space of the UE according to thefirst exemplary embodiment with reference to Equations (1) and (2). TheUE is capable of acquiring a CCE index for blind demodulation of thecontrol channel transmitted by the eNB using Equation (3). Y_(k) denotesa random variable for distributing the control channels regularly acrossthe entire control channel region by user in order to avoid collision.Y_(k) varies at every subframe according to Equation (2). The searchspace for the first control channel group can be expressed as Equation(3):

L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i,

m=0, . . . ,M ^((L))−1,i=0, . . . ,L−1

for common control channel with antenna port set #1

and Y _(k)=(A·Y _(k-1))mod D  (3)

where Y_(k) denotes a common UE IDentifier (ID); and A and D are 39827and 65537, respectively.

The search space for the second control channel group can be expressedas Equation (4):

L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i,

m=0, . . . ,M ^((L))−1,i=0, . . . ,L−1

for UE specific control channel with antenna port set #2

and Y _(k)=(A·Y _(k-1))mod D  (4)

where Y_(k) starts with the dedicated UE identifier (ID); and A and Dare 39827 and 65537, respectively.

According to Equations (3) and (4), the search spaces are determinedwith different values of Y_(k). The first group is determined with theUE group identifier, and the second group is determined with a unique UEidentifier. That is, the control channel region for multiple UEsconfigured at the same location but varies continuously at everysubframe. The UE-specific control channels for the respective UEs aretransmitted at random positions. In this way, it is possible to avoidrepeated collisions.

FIG. 5 is a diagram illustrating a mechanism of control channeldetection according to a second exemplary embodiment of the presentinvention. Referring to FIG. 5, the eNB according to the secondexemplary embodiment of the present invention configures differentcontrol channel transmission resources and maps the logical controlchannel resources thereto respectively using the same search space. TheeNB transmits the control channels mapped to the resources usingdifferent reference signals or different reference signal ports. Theterminal receives the control channels mapped to the different controlchannel regions in the same search space using the different referencesignals or different reference signal ports.

The second exemplary embodiment of the present invention can be appliedto the UE which is capable of receiving both the legacy control channeland the newly introduced control channel. The legacy control channel 501transmitted in the control channel region and the new control channel509 transmitted in the new control channel region are depicted in theFIG. 5. The control channels 501 and 509 are coded by the respectiveencoders 503 and 511. The control channel 501 is transmitted via antenna507 using the reference signal or reference signal group 505 that hasbeen indicated to the UE. Here, the control channel 501 may betransmitted with CRS generated by a CRS generator. The eNB transmits thecontrol channel 509 in the new control channel region 513 notified tothe UE in advance through higher layer signaling. The eNB transmits thecontrol channel 509 via antenna 521 using the reference signal orreference signal group 515 that has been indicated to the UE. Herein,the new control channel region 513 and the reference signal or referencesignal group 515 are collectively denoted as 517. In another example,the eNB transmits the control channel 509 via antenna 521 as precoded bythe precoder 419.

Such a control channel structure is designed to transmit the controlchannel in the legacy control channel region and the new control channelregion dynamically. The eNB is capable of transmitting the controlchannels in the legacy control channel region in the case where thechannel condition of the UE is bad or in the new control channel regionin the case where the channel condition is good. This method isadvantageous in that the eNB is capable of changing the transmissionregion of the control channel without extra signaling. Also, this methodis advantageous in that the UE is capable of receiving the controlchannel by applying the same search space to different resources withoutadditional search space configuration. That is, the method of the secondexemplary embodiment allows the UE to receive the control channelsmapped to the different resources in the same search space withdifferent reference signals.

If the eNB transmits the control channels, the UE configures the logicalcontrol channel resource 523. The common control channel is received inthe common control region 525. Each UE determines UE-specific controlchannel regions 529, 527, and 531 using Equation (1) for search spacedetermination. Afterward, the UE maps the control channel region 533 forPDCCH transmission to the logical control channel region 535 to receivethe common control channel and UE-specific control channel with CRS. Atthe same time, the UE maps the resource region 537 for ePDCCHtransmission to the logical control channel region to receive the ePDCCHin the UE-specific control channel region 539. The UE receives theePDCCH using the pre-notified reference signal group 515. In the case ofePDCCH, the resource 533 to which it is actually mapped may have adifferent resource value. In contrast, the resource 533 to which thePDCCH is mapped has the same resource value. The control channel searchspace for the first control channel group can be expressed by Equation(5):

L·{(Y _(k) +m)mod └N _(CCE,k(PDCCH)) /L┘}+i,

m=0, . . . , M _(PDCCH) ^((L))−1,i=0, . . . ,L−1

for dedicated control with CRS

and Y _(k)=(A·Y _(k-1))mod D  (5)

where Y_(k) starts with the common UE identifier; and A and D are 39827and 65537, respectively.

The search space for the second control channel group can be expressedby Equation (6):

L·{(Y _(k) +m)mod └N _(CCE,k(ePDCCH)) /L┘}+i,

m=0, . . . ,M _(ePDCCH) ^((L))−1,i=0, . . . ,L−1

for dedicated control with configured

DRS antenna port and Y _(k)=(A·Y _(k-1))mod D  (6)

where Y_(k) starts with the common UE identifier; and A and D are 39827and 65537, respectively. M_(PDCCH) ^((L)) and M_(ePDCCH) ^((L)) denotethe numbers of PDCCH and ePDCCH search times, respectively. Theseparameters can be informed through higher layer signaling. According toa modified exemplary embodiment, the numbers of search times for thePDCCH and the ePDCCH can be stored in the memories of the UE and the eNBin advance.

FIG. 6 is a diagram illustrating a mechanism of a control channeldetection according to a third exemplary embodiment of the presentinvention. The eNB according to the third exemplary embodiment of thepresent invention configures a plurality of control channel transmissionresources and notifies the UE of reference signals or reference signalgroups for use in association with the respective resources. The UEconfigures the plural control channel transmission regions into thesearch spaces based on the reference signals or reference signal groupsinformed by the eNB. The UE receives the control channels based on thereference signals or the reference signal groups mapped to theresources.

The control channels can be sorted into two groups 601 and 613. The twocontrol channel groups 601 and 613 are the groups of certain controlchannels and are coded by the respective encoders 603 and 615. The eNBis capable of configuring such that the control channels are selectivelytransmitted via antennas 611 and 623 in the two control channel groupsusing the reference signals or reference signal groups 607 and 619. TheeNB notifies the UE of the reference signals or reference signal groups607 and 619 used in resource regions commonly and independently. Theresource region 605 for transmitting one control channel group and thereference signal therefor and the resource region 617 for transmittinganother control channel group and reference signal therefor are depictedin the drawing. Here, resource regions 605 and 617, and referencesignals or reference signal groups 607 and 619, are collectively denotedas 625. In another example, the two control channel groups 601 and 613may be transmitted via antennas 611 and 623 as precoded by precoders 609and 621.

The two resources 627 and 629 are the resources determined according tothe resource configuration method or transmission method. For example,one resource can be the resource 639 for transmitting the interleavedcontrol channels while the other resource can be the resource 641 fortransmitting the non-interleaved control channels. According to anotherexemplary embodiment of the present invention, one resource can be thecontrol channel region 643 for the distributed transmission mode, whilethe other resource can be the control channel region 645 for thelocalized transmission mode. The eNB can configure the resource regionssuch that the UE is capable of receiving the control channelsefficiently with or without application of the multiple antennatransmission mode.

According to the third exemplary embodiment of the present invention,two resources can be configured into a distributed transmission resourceor an interleaving transmission resource and a localized transmissionresource or a non-interleaving transmission resource. The two resourcescan be configured independently or in an overlapped manner. In the casewhere the control channels are transmitted on the two resources, the eNBperforms transmission with different reference signals for the tworesources. The UE is capable of receiving the control channels withdifferent reference signals for the respective resources. Using theresources configured with different reference signals, the eNB iscapable of configuring different transmission modes for the respectiveresource regions. The eNB is capable of transmitting the controlchannels to achieve at least one of frequency diversity gain and antennadiversity gain according to the channel condition of the UE. In thismanner, the eNB is capable of supporting both the resource configurationand multi-antenna transmission mode simultaneously and switching amongthe transmission resources and among the transmission modes dynamically.

Typically, the distributed transmission region or the interleavingtransmission region can be used for transmitting the common controlchannel 631 or the UE-specific control channel 633 for the UE operatingin a TD transmission mode. In contrast, the localized transmissionregion or the non-interleaving transmission region can be used fortransmitting the dedicated reference signals 635 and 637 in thebeamforming mode. However, the transmission method can be changeddepending on the number of UEs, eNB status, and UE status. The searchspace for the first control channel group can be expressed by Equation(7):

L·{(Y _(k) +m)mod └N _(CCE,k(Localized)) /L┘}+i,

m=0, . . . ,M _(Localized) ^((L))−1,i=0, . . . ,L−1

with DRS port set 1

and Y _(k)=(A·Y _(k-1))mod D  (7)

where Y_(k) starts with the dedicated UE ID; and A and D are 39827 and65537, respectively.

The search space for the second control channel group can be expressedby Equation (8):

L·{(Y _(k) +m)mod └N _(CCE,k(distributed)) /L┘}+i,

m=0, . . . ,M _(distributed) ^((L))−1,i=0, . . . ,L−1

with DRS port set 2

and Y _(k)=(A·Y _(k-1))mod D  (8)

FIG. 7 is a flowchart illustrating a control channel transmission methodof the eNB according to an exemplary embodiment of the presentinvention.

Referring to FIG. 7, the eNB transmits the configuration information ofePDCCH through higher layer signaling at step 701. This informationincludes at least one resource information and at least one referencesignal information for ePDCCH transmission as proposed in the presentdisclosure. The eNB configures the control channels of PDCCH and ePDCCHat step 703. Next, the eNB configures the search spaces as the controlchannel transmission regions for the control channel groups transmittedwith multiple antenna port sets and arranges the control channels in thesearch regions so as to avoid collision between UE-specific controlchannels at step 705. The eNB transmits the control channels with therespective reference signals in order for the UEs to receive the controlchannels addressed thereto at step 707.

FIG. 8 is a flowchart illustrating a control channel reception method ofa UE according to an exemplary embodiment of present invention.Referring to FIG. 8, the UE receives the information about ePDCCHthrough higher layer signals at step 801. This information may includethe control channel region information and at least one reference signalinformation for receiving on the respective resources. The UE estimatesthe channels based on the reference signals and receives the informationon the control channel region in the data region based on the respectivereference signals at steps 809 and 803. The UE configures the searchspaces in the data region determined with the reference signal at steps811 and 805. The UE demodulates the control channel of one controlchannel resource region at step 811 and another control channel resourceregion at step 805. The UE receives the control channel informationusing the demodulated control channel at step 807.

FIG. 9 is a block diagram illustrating a configuration of a controlchannel transmission apparatus of an eNB according to an exemplaryembodiment of the present invention.

Referring to FIG. 9, the scheduler 917 controls the PDCCH generator 905and the ePDCCH generator 907 to configure the control channels based onthe control channel information 901. The precoder 919 performs precodingon the ePDCCH, PDSCH 909, DRS 911, and CRS 913 according to thetransmission mode. The resource mapper 921 maps the control channels tothe reference signals using the precoded signal. The Frequency Domain(FD) multiplexer 923 multiplexes the data channel and ePDCCH accordingto the scheduling information of the scheduler 917. The resource mapper915 maps the PDCCH and CRS 903 to the resource. The Time Domain (TD)multiplexer 925 multiplexes the multiplexed ePDCCH and PDSCH signal withmultiplexed PDCCH signal in the time domain. The transmitter 927transmits the time domain-multiplexed signal to the UE.

FIG. 10 is a block diagram illustrating a control signal receptionapparatus of a UE according to an exemplary embodiment of the presentinvention.

Referring to FIG. 10, the receiver 1001 receives a signal. The TDdemultiplexer 1003 demultiplexes the received signal into PDCCHtransmission region and PDSCH transmission region. The channel estimator1007 estimates channels using the CRS 1005 in the PDCCH transmissionregion. The PDCCH receiver 1009 receives PDCCH, and the control channeldetector 1011 detects the received PDCCH. The FD demultiplexer 1021demultiplexes the PDCCH region. The resource de-mapper 1023 delivers thePDSCH to the PDSCH receiver 1015, the ePDCCH to the ePDCCH receiver1013, and CRS 1025 and DRS 1017 to the channel estimator 1027. Thechannel estimator 1027 estimates channels. The PDSCH decoder 1019 andthe control channel detector 1011 receive the control channel using theestimated control channel information.

According to an exemplary embodiment of the present invention, the eNBis capable of transmitting to the UE the control channels using multipledifferent reference signals with various transmission modes in order toachieve frequency selective gain or frequency diversity gain dependingon the channel conditions experienced by the UE. The UE is capable ofconfiguring the search spaces for receiving the control channelsaccording to the type of reference signal and/or allocated resource andreceiving the control channels based on the channel estimationinformation. The UE is capable of receiving the control channelstransmitted in various transmission modes simultaneously without extrasignaling. The eNB is capable of transmitting the control channels withdifferent reference signals or in different transmission modes accordingto the types of the control channels.

As described above, the control channel detection method and apparatusof the exemplary embodiments of the present invention are advantageousto transmit/receive control channels efficiently with differentreference signals or in different transmission modes.

It will be understood that each block of the flowchart illustrationsand/or block diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks. These computer programinstructions may also be stored in a non-transitory computer-readablememory that can direct a computer or other programmable data processingapparatus to function in a particular manner, such that the instructionsstored in the computer-readable memory produce an article of manufactureincluding instruction means which implement the function/act specifiedin the flowchart and/or block diagram block or blocks. The computerprogram instructions may also be loaded onto a computer or otherprogrammable data processing apparatus to cause a series of operationalsteps to be performed on the computer or other programmable apparatus toproduce a computer implemented process such that the instructions whichexecute on the computer or other programmable apparatus provide stepsfor implementing the functions/acts specified in the flowchart and/orblock diagram block or blocks.

Furthermore, the respective block diagrams may illustrate parts ofmodules, segments or codes including at least one or more executableinstructions for performing specific logic function(s). Moreover, itshould be noted that the functions of the blocks may be performed in adifferent order in several modifications. For example, two successiveblocks may be performed substantially at the same time, or may beperformed in reverse order according to their functions.

The term “module” according to the exemplary embodiments of the presentinvention, means, but is not limited to, a software or hardwarecomponent, such as a Field Programmable Gate Array (FPGA) or ApplicationSpecific Integrated Circuit (ASIC), which performs certain tasks. Amodule may advantageously be configured to reside on the addressablestorage medium and configured to be executed on one or more processors.Thus, a module may include, by way of example, components, such assoftware components, object-oriented software components, classcomponents and task components, processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,microcode, circuitry, data, databases, data structures, tables, arrays,and variables. The functionality provided for in the components andmodules may be combined into fewer components and modules or furtherseparated into additional components and modules. In addition, thecomponents and modules may be implemented such that they execute one ormore CPUs in a device or a secure multimedia card.

The foregoing disclosure has been set forth merely to illustrate theexemplary embodiments of the present invention and is not intended to belimiting. Since modifications of the disclosed embodiments incorporatingthe spirit and substance of the invention may occur to persons skilledin the art, the invention should be construed to include everythingwithin the scope of the appended claims and equivalents thereof.

Although exemplary embodiments of the present invention have beendescribed in detail hereinabove with specific terminology, this is forthe purpose of describing particular embodiments only and not intendedto be limiting of the invention. While particular embodiments of thepresent invention have been illustrated and described, it would beobvious to those skilled in the art that various other changes andmodifications can be made without departing from the spirit and scope ofthe invention.

What is claimed is:
 1. A control channel transmission method of a basestation, the method comprising: acquiring a criterion for sortingcontrol channels; sorting the control channels into at least two controlchannel sets based on the criterion; configuring the control channels byallocating at least one antenna port to each control channel set; andtransmitting the control channels as configured.
 2. The method of claim1, further comprising: determining the criterion; and transmittinginformation on the criterion and antenna ports allocated to each controlchannel set to a terminal through higher layer signaling.
 3. The methodof claim 1, wherein the sorting comprises sorting the control channelsinto the at least two control channel sets by based on controlinformation format.
 4. The method of claim 1, wherein the sortingcomprises sorting the control channels into the at least two controlchannels sets based on transmission mode.
 5. The method of claim 4,wherein the transmission mode comprises at least one of a beamformingtransmission mode, a single antenna transmission mode, and atransmission diversity mode.
 6. A control channel reception method of aterminal, the method comprising: acquiring a criterion for sortingcontrol channels into at least two control channel sets; acquiringallocation information on at least one antenna port allocated to eachcontrol channel set sorted by the criterion; and receiving the controlchannels based on the criterion and allocation information.
 7. Themethod of claim 6, further comprising receiving the criterion andallocation information from a base station.
 8. The method of claim 6,wherein the criterion is control channel format of the control channels.9. The method of claim 6, wherein the criterion is transmission mode ofthe control channels.
 10. The method of claim 9, wherein thetransmission mode comprises at least one of a beamforming transmissionmode, a single antenna transmission mode, and a transmission diversitymode.
 11. A base station for transmitting control channels, the basestation comprising: a scheduler which acquires a criterion for sortingthe control channels and sorts the controls channels into at least twocontrol channel sets based on the criterion; a control channelinformation generator which configures the control channels byallocating at least one antenna port to each control channel set; and atransmitter which transmits the control channels as configured.
 12. Thebase station of claim 11, wherein the scheduler determines the criterionand transmits information on the criterion and antenna ports allocatedto each control channel set to a terminal through higher layersignaling.
 13. The base station of claim 11, wherein the scheduler sortsthe control channels into the at least two control channel sets bycontrol information format.
 14. The base station of claim 11, whereinthe scheduler sorts the control channels into the at least two controlchannels sets by transmission mode.
 15. The base station of claim 14,wherein the transmission mode comprises at least one of a beamformingtransmission mode, a single antenna transmission mode, and atransmission diversity mode.
 16. A terminal for receiving controlchannels, the terminal comprising: a controller which acquires acriterion for sorting control channels into at least two control channelsets and acquires allocation information on at least one antenna portallocated to each control channel set sorted by the criterion; and areceiver which receives the control channels based on the criterion andallocation information.
 17. The terminal of claim 16, wherein thereceiver receives the criterion and allocation information from a basestation.
 18. The terminal of claim 16, wherein the criterion is controlchannel format of the control channels.
 19. The terminal of claim 16,wherein the criterion is transmission mode of the control channels. 20.The terminal of claim 19, wherein the transmission mode comprises atleast one of a beamforming transmission mode, a single antennatransmission mode, and a transmission diversity mode.